Tanning process and product produced thereby



'Patented Oct. 2, 1934 v PATENT OFFICE" UNITED STATES TANNING PROCESS AND PRODUCT PRODUCED THEREBY No Drawing.

Application October 28, 1932,

Serial No. 640,053 4 Claims. (01. 149' 5) My invention relates to process for tanning hides and skins and refersparticularly to the taming of hides and skins by means of ureaaldehyde compounds.

5, Numerous processes are employed in the tanning of hides and skins among which are processes employing oils, vegetable tannins, alum,

chrome, synthetic tannins and formaldehyde.

In general, these tanning processes do not possess the properties of producing leather of good fullness of feel and having good resistance to alkalies, acids and hot water, all of which properties are desirable, particularly in the production of washable white leather.-

I have found, however, that the above mentioned, and other objectionable features of the present employed methods of tannage can be overcome by using urea-aldehydes as the tanningmedium. I have found that certain compounds of urea and aldehydes can be employed for the tanning of hides and skins, producing leather, and especially white leather, possessing valuable and desirable physical attributes.

If urea and an aldehyde, for instance formaldehyde, are allowed toreact upon each other in an aqueous solution, there is finally formed an insoluble compound, or condensation product, which has some values for tanning purposes. I have found, however, that if this aqueous. solution of urea and formaldehyde, for instance, be employed, prior to the formation of the insoluble product, valuable tanning results will be obtained, which are of much better penetration the insoluble compounds. 1

As far as I have been able to determine fro the literature, and from my own experiments, the chemical reactions incident to the combinations of urea and 'aldehydes are not'fully known, and, hence I am compelled to refer to the products, or compounds, thus produced in a descriptive, rather than a chemical, manner.

I have found for, instance if I prepare asolu- 'tion of 3 ounces of urea, 1%; ounces of formaldehyde, 2 ounces of sodium carbonate and 16 ounces of sodium chloride per gallon of water, and use this solution before the formation of the water-insoluble compound for taming purposes, most excellent results are obtained.

In my urea-aldehyde tanning process, I prefer to use a so-called "retarding compound in the first stages of the operation and an accelerator in the latter steps of the tanning process. I

and more uniform than those produced with results.

prefer also to employ a so-called buffer compound in the'tanning bath.

. While these compounds are not absolutely necessary their employment results in improved Among the retarding compounds which I have found suitable for use in my process are the alkali-metal sulphite compounds, such as sodium bisulphite, sodium sulphite, sodium hydrosulphite and sodium hyposulphite.

Among the accelerators I have found useful with my process are acids, among which are sulphuric acid, nitric acid, hydrochloric acid,

.-formic acid and oxalic acid; highly acid salts,

among which are sodium bisulphate, aluminum sulphate and other compounds which will produce an acid reaction in my process.

Among the buffers suitable for employment,

that is compounds which resist a change in the pHvalue of the solution and repress ionization are potassium citrate, sodium acetate, trisodium phosphate, disodium phosphate, and stabilizers, such as ethyl alcohol, methyl alcohol and glycerol.

By urea-aldehyde compounds, I mean those water-soluble compoundsformed by the aqueous interaction of urea and substituted urea, as thiourea, with aldehydes, or substituted aldehydes among which are formaldehyde, acetaldehyde, butyl aldehyde, and benzaldehyde'. This group of compounds includes those formed from equal moles of urea, or a substituted urea, and an aldehyde, and those formed from unequal moles of the two groups of chemicals. Y

I give the following as an example for the production of a full, well filled, washable white leather obtainable by my process:,-

The hides, skins or pelts are prepared by any suitable and well known process and then immersed in a solution containing approximately 20% of a urea-formaldehyde solution and 10% of salt at about 35 C. and gently agitated for about 5 hours. The temperature may then be raised to 45 C, and the solution acidified to about pH3 with sulphuric acid and agitation continued for 30 minutes. The temperature is then raised to 55 C., the skins worked for 15 minutes, cooled, rinsed in cold water, neutralized with sodium bicarbonate, rinsed, fat liquored and dried.

One method of producing the urea-formaldehyde solution mentioned in the above example is as follows, 3 ounces of urea, 1 ounces formaldehyde, 2 ounces sodium carbonate and 16 ounces of sodium chloride are dissolved per gallon of water, and this solution employed in the tanning process at once, or at least prior to the formation of an insoluble precipitate.

My invention as herein described is not directed to any particular method of producing a ureaaldehyde' compound, and hence methods other than that above described may be employed for its production.

A retarding compound for the formation of the mentioned precipitate may be added to'the original tanning liquor if desired and a bufier compound can also be added to the tanning liquor. I

The urea employed can be substituted by an equal molecular quantity of thio urea, and by the words urea compound in my specification and claims I mean a member of the group consisting of urea and urea substituted compounds.

My invention, therefore, presents a most valuable advance in tanning processes, and as the chemicals, quantities, times, temperatures and steps of procedure must necessarily vary with the character of the hide, skin or pelt being tanned and the particular results desired, I do not limit myself to those specifically mentioned, as these are given simply as a means for clearly describing my invention.

What I claim is:-

1. In a process for tanning hides, skins and pelts, the step which comprises treating said materials with a solution containing 'aretarding compound and a water-soluble compound resulting from the aqueous interaction of equal mols of a urea compound and an aldehyde.

2. In a process for tanning hides, skins and pelts, the step which comprises treating said materials with a solution containing a retarding compound and a water-soluble compound resulting' from the aqueous interaction of equal mols RALPH E. PORTER. 

